This invention relates to grating structures and methods of making the grating structures. In addition, the invention relates to transmission gratings and methods of making transmission gratings.
Gratings and prisms are typical examples of optical elements used to separate light according to wavelength or combine light from different sources into a single beam. There are a wide variety of applications for such optical elements including, for example, applications in optical telecommunications, data communications, and spectroscopic analysis of gases, liquids, and solids. Additional examples are illustrated in PCT Patent Application Publication No. WO 00/40935, incorporated herein by reference. With respect to gratings, there are a number of parameters to consider when designing a grating for a particular application. Grating design parameters include, for example, the material used for the grating, the type of grating (e.g., sinusoidal, triangular, blazed, or square/rectangular well), and the physical dimensions of the grating (e.g., the period of the grating, the depth of the grating, and the duty cycle of square/rectangular well gratings). All of these parameters can influence the amount of light that is diffracted by the grating, the efficiency of diffraction into a particular diffraction order, and the efficiency of diffraction for a particular polarization of light (e.g., transverse electrical (TE) or transverse magnetic (TM) polarizations).
The efficiency of diffraction for a particular condition (e.g., order, polarization, or both) can be defined as the ratio or percentage of the intensity of light diffracted for that condition versus the intensity of light incident on the grating. For example, efficiency of diffraction into a particular order can be defined as the ratio or percentage of the intensity of light diffracted into that order versus the intensity of light incident on the grating. Other measures of diffraction efficiency, such as diffraction efficiency for a particular polarization of light, can be determined using this general definition.
Gratings can be designed for a variety of purposes and to achieve a variety of design and application objectives. In some embodiments, it is desirable to obtain high efficiency of diffraction into a single diffraction order. In some embodiments, it is desirable to obtain similar efficiency for TM and TE polarizations of light. In some embodiments, it is desirable to produce a structure that provides the grating with at least partial protection from contamination and damage. In some embodiments, it is desirable to provide the grating with passive temperature compensation to reduce or eliminate the temperature dependence of the output light of the grating.
Generally, the present invention relates to grating structures and methods of making the grating structures. One embodiment is a transmission grating. The transmission grating includes a first piece and a second piece. The first piece has a surface defining a grating structure. The second piece is bonded to the surface of the first piece to encapsulate the grating structure.
Another embodiment is a method of making a transmission grating. A grating structure is formed in a surface of a first piece. A second piece is bonded to the surface of the first piece to encapsulate the grating structure. One example of such a method includes treating (e.g., plasma or acid treating) at least one of the surface of the first and second pieces (and preferably a surface of both the first and second pieces) to form reactive groups. These reactive groups can then be used to bond the two pieces together. Optionally, a high temperature anneal is performed after the initial bonding.
Yet another embodiment is a transmission grating that includes a piece having a surface defining a grating structure. The grating structure has multiple wells that have an average aspect ratio (depth:width) of at least 7:1. Deeper wells with aspect ratios of at least 10:1 and 15:1 can be formed. In some instances, such grating structures can provide individual diffraction efficiencies for TE and TM polarized light of at least 85% or 95% or more.
Yet another embodiment is a transmission grating that includes a piece having a surface defining a grating structure. The grating structure provides individual diffraction efficiencies for TE and TM polarized light of at least 90% or more.
Another embodiment is a method of making a transmission grating. A masking layer disposed on a substrate is patterned to expose multiple regions, corresponding to grating lines, of a surface of the substrate. These regions of the substrate are etched to form multiple wells in the substrate. The wells have an average depth:width aspect ratio of at least 3:1 and the average width of the wells at the surface of the substrate is typically no more than 1000 nm. Deeper wells with aspect ratios of at least 7:1, 10:1, and 15:1 can be formed.
Another embodiment is a method of forming a grating structure. A waveguiding layer is formed on a substrate. A portion of the waveguiding layer is removed to form a grating structure that includes multiple wells that are spaced apart and have a substantially uniform period.
Yet another embodiment is a method of forming a grating structure. A first grating structure is formed in a surface of a first piece of dielectric material. A second grating structure is formed in a surface of a second piece of dielectric material so that the first and second grating structures having a substantially similar grating periods. The first piece is disposed over the second piece with the first and second grating structures adjacent. An interference pattern between the first and second grating structures is observed. At least one of the first and second grating structures is moved based on the interference pattern to register the first and second grating structures.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.